<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        
        body,
        html {
            height: 100%;
        }
        /* .box {
            height: 100%;
            display: flex;
        }
        
        .left {
            width: 200px;
            border: 1px solid red;
        }
        
        .right {
            flex: 1;
            border: 1px solid blue;
        } */
        /* 使用浮动 */
        
        .box {
            height: 100%;
            overflow: hidden;
        }
        
        .left {
            width: 200px;
            height: 100%;
            float: left;
            border: 1px solid red;
        }
        
        .right {
            margin-left: 200px;
            height: 100%;
            border: 1px solid blue;
        }
    </style>
</head>

<body>
    <div class="box">
        <div class="left">left</div>
        <div class="right">right</div>
    </div>
</body>

</html>